US 20060138696 A1
The invention relates to a method and a device for the secondary treatment and the cooling of preforms (10) once they have been removed from the open mould halves (18, 9) of an injection moulding machine. The preforms are removed from the open moulds (18, 9) while still hot, by means of water-cooled cooling sleeves (21) of a removal device (11), and are subjected to intensive cooling during the duration of an injection moulding cycle. Both the entire inner side and the entire outer side of the blow-moulded part (10) are subjected to intensive cooling. Secondary cooling is then carried out, the duration thereof being equal to a multiple of the duration of an injection moulding cycle. After being removed from the casting moulds, the preforms are dynamically introduced into the cooling sleeves (21) until they fully touch the walls thereof. The inner cooling is carried out in a time-delayed manner.
22. A method of manufacturing a preform, comprising:
injection molding the preform in an open mould half of an injection molding machine;
removing the preform from the open mould half of the injection molding machine in a hot state via a removing device;
physically contacting the preform with a cooling sleeve via the removing device by moving the preform in a substantially linear manner, an inner surface of the cooling sleeve substantially corresponding to an outer surface of the preform;
after the step of removing, cooling an inner portion of the preform via a cooling pin and an outer portion of the preform via the cooling sleeve; and
after the step of cooling, further cooling the preform;
wherein a duration of the further cooling is substantially a multiple of a duration of the injection molding.
23. The method of
24. The method of
25. The method of
26. The method of
27. The method of
28. The method of
29. The method of
30. The method of
31. The method of
32. The method of
33. The method of
34. The method of
35. The method of
36. The method of
37. The method of
38. The method of
39. The method of
40. The method of
41. A device for cooling a preform after the preform has been removed from an open mould half of an injection molding machine, comprising:
a cooling pin configured to be introduced into the preform and cool an inner portion of the preform;
a removal station including a cooling sleeve, the cooling sleeve having an inner surface which substantially corresponds to an outer surface of the preform, the cooling sleeve being configured to cool an outer portion of the preform;
a removal device configured to remove the preform from the open mould half of the injection molding machine and place the preform into the cooling sleeve via a substantially linear movement; and
a controller configured to control the movement of the preform.
42. The device of
43. The device of
44. The device of
45. The device of
46. The device of
47. The device of
48. The device of
49. The device of
wherein the elastic seal is configured to form a substantially airtight seal with an inner surface of the preform so as to allow a swelling pressure to be generated inside the preform.
50. The device of
51. The device of
52. The device of
53. The device of
54. The device of
a blast mandrel having a tubular extension, the tubular extension including a blast air boring; and
a contact head movable relative to the tubular extension, the contact head including a blast chamber in flow communication with the blast air boring.
55. The device of
56. The device of
wherein the one of the source of blast air and the compression spring is configured to generate the controlled force.
57. The device of
58. The device of
59. The device of
60. The device of
61. The device of
62. The device of
The invention relates to a method for the secondary treatment and cooling of preforms after they have been removed from the open mould halves of an injection moulding machine, with the preforms being removed from the open moulds while still hot by means of water-cooled cooling sleeves of a removal device. The invention furthermore relates to a device for the secondary treatment and cooling of preforms after the removal from the upper mould halves of an injection moulding machine by means of water-cooled cooling sleeves of a removal device.
In the production of injection moulds, the cooling time is a determining factor for the total time of a full cycle. The main cooling preformance occurs still in the casting mould halves. Both casting mould halves are intensively water-cooled during the casting process so that the temperature of the injection moulds can be lowered already in the forms from approximately 280° C., at least in the border layers, to a range of 70° C. to 120° C. In the outer layers, the so-called glass temperature of approx. 140° C. is passed very quickly. In recent history, the actual casting process up to the removal of the injection moulds could be lowered to about 12 to 15 seconds in the production of thick-walled preforms, and to less than 10 seconds for thin-walled preforms, and this at optimal qualities with respect to the still semi-rigid preforms. The preforms have to set sufficiently in the mould halves so they can be gripped with relatively high force by the ejection aids and transferred to a removal device without deformation and/or damages. The form of the removal device is adapted to the outer dimensions of the injection moulds. For casting mould halves with high wall strength, the intensive water cooling is performed from outside to inside and due to physical reasons with a significant time-delay. This means that the aforementioned 70° C. to 120° C. cannot be reached uniformly across the entire diameter. As a result, there is a quick re-warming over the cross-section of the material from inside to outside as soon as the intensive water cooling is interrupted by the moulds. The secondary cooling is extremely important for two reasons. First, mould changes should be avoided until dimensional stability has been reached, as should damage to the surface, such as pressure points, etc. Secondly, if cooling in the higher temperature range is too slow, it may lead to re-warming and the local formation of damaging crystals, which must be avoided. The objective is an evenly amorphous condition in the material of the finished preform. The residual temperature should be low enough that there is no adhesive damage at the contact points in the relatively large packing drums with thousands of loosely poured parts. Even after a slight re-warming, the injection moulds must not exceed a surface temperature of 40° C. The secondary cooling after the preforms have been removed from the injection mould is as important as the primary cooling in the casting moulds.
U.S. Pat. No. 4,592,719 (Bellehache et al.) proposes to increase the production rate of the preforms by using atmospheric air for the cooling. The air is used as cooling air during the transport and/or the “handling” with maximum cooling effect at the preforms by specifically guiding the flow, on the inside as well as on the outside. A removal device having as many suction pipes as parts produced in an injection cycle enters between the two open mould halves. The suction pipes are then slid over the preforms. At the same time, air starts to flow into the area of the entire circumference of each blow-moulded part through a suction line so that said blow-moulded parts are cooled with the outside air from the moment they enter the suction sleeve. After all of the injection moulds of a casting cycle have been removed, the removal device leaves the travel space of the mould halves. The mould halves are immediately free and are closed again for the subsequent moulding cycle. After the move-out movement, the removal device pivots the preforms from a horizontal into a vertical position. At the same time, a transfer device moves into a precise pick-up position over the removal device. The transfer device has the same number of inner grippers as there are suction pipes on the removal device. In sufficient time after the transfer of all injection moulds and before the mould halves open again, the removal device is pivoted back into its feed position so that the next batch of injection moulds can be removed from the moulds. In the meantime, the transfer device transfers the injection moulds to a transporter and returns to the pickup position for the next batch without the preforms.
With WO 00/24562 (Netstal), which is an older application filed by the applicant, the focus is on the handling, i.e., on avoiding malfunctions such as stuck injection moulds and corresponding double inserts, and thus increasing the productivity at an optimum cooling effect.
The object to be attained by EP 0 947 304 (Husky) was to improve the cooling efficiency and the quality of the preforms and to shorten the entire cycle time. The specification describes first and foremost the problem of crystal formation as a result of poor secondary cooling. It is proposed to cool primarily the inner mandrel part with air with a controlled and automatically guided blast nozzle. The cooling starts immediately after the preforms have been removed from the open mould halves, which is supposed to prevent the local formation of crystals.
U.S. Pat. No. 6,332,770 (Husky) solves the same problem as EP 0 947 304, but with cooling through a local convection cooling effect. A mandrel cooled on the inside is introduced into the inner mandrel area. In doing so, primarily the mandrel area of the preforms is treated with convective cooling. The big disadvantage of the proposal concerning the convective contact cooling by means of a mandrel that can be introduced into the preform is the problem of a precise, automatic mechanical introduction of the mandrel until contact has been made with the respective interior wall surface of the preforms, and furthermore primarily the required precision for the introduction of 100 and more mandrels. The entire machine and all of its movements must be developed with the utmost precision so that each individual preform is contacted in the same way and without pressure damage.
A very interesting solution for the secondary cooling of preforms after they have been removed from the production tool is described in JS-PS 8-103948 (Footier K K). It has been realized that a complete cooling of the preforms still in the production tool prolongs the entire injection cycle. The forms have to be opened much later, thus reducing the productivity extensively. Therefore, a completely separate secondary cooler is proposed for the still hot preforms after they are removed from the production tool. In this way, a high cooling efficiency could be reached with a simple construction. The preforms are transferred to a secondary preform cooler having a corresponding number of cooling pins. In this way, each preform is cooled simultaneously inside as well as outside. The inner cooling is performed through the cooling pins, which have an inside blast air channel. The relative movement for the introduction of the cooling pins is performed automatically by a removal robot. The cooling pins have a blast air opening at the very tip. The air blast is aimed directly vertically to the mandrel-shaped closed bottom of the preforms and can then be guided in opposite direction along the inner wall of the preform and flow out freely at the open end of the preform. This solution allows the shortest possible injection moulding cycle time, a very high efficiency of the overall production, and it prevents any crystallization, in particular in the gate area and thus allows the production of preforms of the highest quality with optimum efficiency.
Each of the solutions shown above has its own advantages. However, these advantages come at the expense of specific limitations or greater efforts. In addition to avoiding the formation of crystals, one important goal in the secondary cooling of preforms is the optimum shape retention. In the scope of secondary cooling, there is the risk that the preforms bend and are no longer completely axially symmetrical. The result may be that individual preforms get stuck in the secondary cooler, thus creating so-called double inserts. This means that a second preform is introduced into the same cooling sleeve. Experience has shown that the complete secondary cooling can be divided into two segments, i.e., in a first phase directly after the removal of the preforms from the mould halves and a second phase in the relatively long secondary cooling. The critical phase is actually the first phase, which has a significant influence on the final quality of the preforms. One important recent finding is that the goal is not to completely prevent the formation of crystals, but rather to keep the crystalline portion in the entire preform to a minimum.
The problem to be solved by the new invention was to optimize the cooling in view of a shortened injection moulding cycle time and to obtain the maximum quality and the smallest possible crystal formation in the preforms without significant process technology efforts or additional expenses for the production of the injection moulding machine.
The method in accordance with the invention is characterized in that the preforms are subjected to an intensive cooling during the duration of one injection moulding cycle, which includes the entire inside as well as the entire outside of the blow-moulded part, followed by a secondary cooling that is a multiple of the duration of one injection moulding cycle, with the preforms being introduced dynamically after the removal from the casting moulds until they fully touch the wall of said cooling sleeves and the inner cooling is carried out in a time-delayed manner.
The device in accordance with the invention is characterized in that it has a station for intensive cooling as well as a secondary cooling station, and the intensive cooling station has cooling pins which can be introduced into the inside of the preforms for an inner cooling, with the inner form of the cooling sleeves being adapted to the corresponding inner form of the casting moulds in such a manner that the preforms can be introduced into the cooling sleeves without play, if possible, after they are removed from the casting moulds until they fully touch the walls of said cooling sleeves.
Experience has shown that the first secondary cooling phase is especially critical because the preforms are not yet dimensionally stable. The risk that the blow-moulded part “bends” slightly from the threaded axis relative to the threaded part is indeed a genuine problem in the phase of removing the preform in laying position with horizontally operating injection moulding machines. This applies in particular if the cooling time inside the injection moulds has been reduced to a minimum and the preforms are still relatively hot and correspondingly soft. If the preforms are in laying position in the first phase of the secondary cooling, they tend to lay downward on the appropriate part of the cooling sleeve. With a better cooling contact in the lower part, the cooling sleeve is cooled stronger in the lower part, causing strains in the preform and a tendency of bending in the preform. If individual preforms suffer slight deformation in the first phase of the secondary cooling during shortened cooling in the casting moulds, the resulting deformation can no longer be corrected in the increasingly set preforms.
The new invention proceeds primarily from the cooling concept where the individual preforms are introduced into the cooling sleeves only with the blow-moulded part during the secondary cooling. In doing so, the threaded parts project past the cooling sleeves. This has the enormous advantage that the preforms are inserted into and removed from the cooling sleeves of the removal device in a linear movement. The new solution proposes an optimal contact with the cooling sleeve in particular in the phase of intensive cooling immediately following the removal from the casting moulds and in this way achieves a quick, maximally intensified temperature drop and stabilization of the preforms in the first secondary cooling phase for the subsequent final cooling. The dynamic introduction of the preforms until they fully touch the walls in the cooling sleeves immediately following the removal of the preforms from the casting moulds, but before the longer final cooling, has significant advantages:
For physical reasons, the cooling effect is the highest when the temperature difference between the hot preforms and cooling sleeves is the highest immediately following the removal from the casting moulds. This is where the forced, flush and full-area contact between the preforms and the inner area of the cooling sleeves results in the optimum gain because of the optimized thermal conduction. Thus, the formation of crystals is reduced to a minimum. After the preforms are removed from the casting moulds, said preforms, which are still hot, are introduced into a cooling sleeve with as little play as possible to retain the geometrical accuracy. The preform that is cooled quickly after removal thus retains geometrical accuracy with respect to the symmetry in the subsequent handling.
The first pressing tests already showed that the new solution allowed for a shorter injection cycle time of half a second while completely retaining the quality parameters, which corresponds to an approximately 5% increase in productivity. This is because the preforms are removed from the moulds at a higher temperature, and thus more quickly than with the state of the art. In the very first phase of the secondary cooling, the contact of the still soft blow-moulded part at the inner wall of the cooling sleeves is possible with minimal compressed air forces.
With the new invention, the inner cooling with the cooling pins can be performed with suction air and/or compressed air, with suction air and compressed air being turned on and off through control valves. It is in particular preferred to carry out the inner cooling by means of cooling air with cooling pins arranged on a controllably movable supporting plate, which are introduced synchronically into the inside of the preforms after the removal device has completely moved out and with the cooling air being actively blown in and/or suctioned off. The movement of the cooling pins is carried out synchronously in the timely rhythm of the injection moulding cycle and the introduction movement is performed with power control and/or displacement control.
The inner diameter of the cooling sleeve is selected at most a few hundredths of a millimeter larger than the outer dimensions of the still hot preforms. With the direct control of the suction—and/or compressed air, a swelling pressure can be created, and the preform can be brought into complete contact with the entire inner wall area of the cooling sleeve. After the first contact between the preforms and the inner wall area of the cooling sleeves, the surface contact is maintained for several seconds to maximize the cooling effect. At the same time, a calibration effect is generated for each individual preform. In the production of preforms, the calibration effect allows for a production—and quality standard that was not possible in the scope of the state of the art. Shortly after they are removed from the casting mould, the preforms are again pressed into an exact mould so that any dimensional changes after the first critical handling from the casting moulds into the cooling sleeves, in particular a bending of the preforms due to one-sided contact in the cooling sleeve, can be eliminated. With the calibration effect, the preforms can be removed from the moulds even earlier and thus a shorter casting cycle time, as well as an improved first phase of the secondary cooling, can be achieved. This is very advantageous in particular in view of the quickest possible passing through the glass temperature and thus the damaging formation of crystals. The subsequent secondary cooling is less problematic with respect to all qualitative parameters and can be performed in the required time, preforms of the highest quality are produced, and at the same time, the productivity of the injection moulding machine can be increased. The invention allows several embodiments as well as a number of advantageous modifications. Reference is made to the claims 5 to 9 as well as 11 to 22 in that regard.
An especially advantageous first embodiment is characterized in that a slight swelling pressure is generated through the cooling pins. In view of the best possible thermal transition between the preforms and the inner wall area of the cooling sleeves, the objective is to introduce the preforms into the cooling sleeves without play, if possible. A solution in the state of the art is to develop the preforms conically on the outside, with the preforms being only introduced partially initially, pulled in gradually with appropriate negative pressure at the opposite side, and good wall contact with the cooling sleeve is maintained over the entire duration of the secondary cooling time. The big disadvantage is that the bottom parts of the preforms are cooled only very poorly from the outside. With the new solution, the complete introduction is performed dynamically with no time delay, if possible, i.e. essentially within seconds. The wall contact can be maintained during the remainder of the intensive cooling with the slight swelling pressure. To generate the swelling pressure, each cooling pin has blast air openings and is placed with a slight seal relative to the respective preform. The blast air and the suction air are controlled so that a slight excess pressure is generated in each preform during the intensive cooling, and the preform is pressed to the inner walls of the cooling sleeves and thereby calibrated.
An important goal of the new solution is that the cooling application is carried out gradually during the intensive cooling. The temperature differences that still exist in the preforms are eliminated as quickly as possible after removal from the casting moulds. At the same time, it is possible to lower the crystalline parts in the entire preform to the lowest possible value, with the preforms being brought into a completely dimensionally stable condition for the subsequent secondary cooling. If the preform already has the best possibly symmetry relative to the entire outer form at the beginning of the secondary cooling, the risk of so called “double inserts” resulting from bent preforms and the corresponding operational malfunctions can be ruled out with near certainty.
According to a second embodiment, the inner cooling is performed by means of suction air through cooling pins arranged on a transfer gripper, which are introduced synchronously into the interior of the preforms after the removal device is moved out completely, with suction air remaining active after the intensive cooling during the transfer of the preforms from the removal device to a separate secondary cooling station until the preforms are transferred to the secondary cooler. During the intensive cooling, each cooling pin remains connected to a vacuum pump that actively suctions off warmed cooling air through the cooling pin. The intensive inner cooling is maintained for at least 2 to 7 seconds of cooling time and/or approximately 3% to 10% of the secondary cooling period until sufficient firmness of the outer skin of the preform. The intensive cooling is only a fraction of the entire secondary cooling. During the intensive cooling, the temperature is lowered on the average by 20 to 40° C. A severe prolonging of the intensive cooling phase is not advantageous because the thermal travel within the preform material cannot be increased.
The cooling pin is developed tubular and has a suction opening at the very tip of the cooling pin, with the cooling pin being introduced far enough into the preform for the intensive cooling so that an open gap for the suctioning of the cooling air remains opposite to the inner mandrel-shaped preform bottom. All cooling pins are part of a supporting plate that can be connected to a vacuum source to suction off cooling air from the interior of the preform. The cooling pins have a casing developed as a base, which on the one hand has blow-out openings for the cooling air and on the other hand can be connected to a compressed air source through the supporting plate, with the casing preferably being guided over less than half of the length of the suction pipe. The supporting plate is developed with two chambers, i.e., a first chamber connected to a compressed air source, with the suction pipe being guided through the second chamber and the first chamber being connected directly to the space between the casing and the suction pipe. Controllable valves are arranged for the suction air as well as for the blow air to optimize the usage. During the phase of the intensive cooling, the suction—as well as the blow air is activated. The zero compression point can be determined by selecting the pressure and the quantity on the suction side as well as on the compressed air side. Optimally, the zero compression point is determined in the suction pipe so that the entire interior space of the preform can be placed under a slight overpressure and thus the calibration effect mentioned earlier is generated.
The new solution has a removal device with cooling sleeves, and a supporting plate of the transfer gripper with a cooling air connections [sic], which can be moved to a tight fit relative to said removal device. According to the number of cooling sleeves, the supporting plate is equipped with cooling pins and sealing rings, which form a seal to one each preform in the inside of the preform to generate a slight swelling pressure on the inside of the preforms. The sealing location is arranged relative to the open end of the preforms and becomes effective only at the end of the introductory movement of the blow mandrels. Preferably, the sealing location is established with a soft packing between the individual cooling pins and the outer edge of the threaded part of the preforms and the edge of the threaded part is held by the elastic sealing.
A third embodiment is characterized in that the device for an interior cooling has cooling pins of a controlled, displaceable supporting plate which can be introduced into the preforms, with the individual cooling pins being developed to yield into the direction of the introduction movement with respect to the preforms so that each cooling pin can be introduced with controlled force until it establishes contact with the inner mandrel part of the preforms. The cooling pins can be developed as blow mandrels and have a movably arranged contact head and a continuous air boring to the contact head, which runs into a blast air chamber between the blow mandrel and the contact head and is variable in size. Advantageously, each cooling pin has a compression spring to generate a controlled pressing power. The cooling pins are developed with a contact cooling head for the mechanical contacting and contact cooling of the corresponding interior mandrel part of the respective preform, with the controlled power being generated through blast air and/or a compression spring. The contact head is preferably developed like a sleeve to move freely on the cooling pin between a maximally extended and retracted position.
As the simplest and most cost efficient structural design, each cooling pin has a movably arranged contact head. In this way, a continually run blast air boring is provided for each of the cooling pins up to the contact head, which runs into a blast air chamber that is variable in size. Each contact head is arranged on the cooling pin to move freely like a sleeve between a maximally extended and retracted position, with the extended position being created by the blast air and/or a compression spring and the retracted position being created by negative pressure. In the area of the tip of the contact, the contact heads can have at least one blast air opening that is connected to the blast air chamber. The tip of the contact can be developed integrally in the gate area of the preform for a completely mechanical contacting of the appropriate innermost part of the mandrel part of the respective preform. Each cooling pin advantageously has a blast mandrel base that can be fixedly attached to the supporting plate and has a tunnel-shaped extension in the direction of the blast air, with the contact head being moveable relative to the tubular extension. The contact head and the base of the blast mandrel are developed at least somewhat cylindrically to create a gap between the cylindrical forms and the interior of the preform to increase the rate of the discharged blast air. Cross-borings may be arranged in the area of the base of the blast mandrel, which can be attached to a vacuum source to ensure a safe removal of the preforms from the cooling sleeves and the transfer to the actual secondary cooler.
The new solution has a secondary cooling station as well as an intensive cooling station, and the inner side of the preform as well as the outer side of the preform can be intensively cooled in the intensive cooling station within the duration of one injection moulding cycle. The intensive cooling station can be developed as a structurally independent controllable removal station or as part of a secondary cooler having a number of cooling sleeves that corresponds to several batches of one injection moulding cycle, in particular preferably four batches. The complete secondary cooling has a control to control all movements for the handling of the preforms and the cooling pins as well as for a cyclically pulsed use of compressed air and suction air, furthermore a removal robot with cooling sleeves, a transfer gripper and the supporting plate with controllable movements relative to the cooling pins, with the preforms being transferred by the transfer gripper following intensive cooling in the cooling sleeves of the transfer robot for complete cooling in the secondary cooler.
Another advantageous embodiment is characterized in that the cooling sleeves that are water-cooled on the outside have an inner form that corresponds to the outer form of the preform including the convex bottom part, and the cooling sleeve including the convex bottom part is developed as thin-walled as possible so that a maximum thermal conduction and/or thermal transfer is established across the entire cooling sleeve and from the cooling sleeve to the outside of the preform during the brief contact.
Depending on the strength of the wall, the casting cycle lasts 10 to 15 seconds and the complete cycle including the complete secondary cooling lasts 30 to 60 seconds. However, the operating efficiency of the machine is determined by the casting cycle time. The calibration occurs during the first phase of the secondary cooling, with 1 to 10 bar of compressed air being blown in in a first phase to generate sufficient swelling pressure, for example 0.1 to 0.2 bar.
Preferably, the cooling of the preforms is not interrupted between removal from the mould halves until the cooling is completed. The cooling pins have an elastomer sealing ring. This ensures that there are no deformation forces acting on the threaded part.
Advantageously, a local cooling and hardening of the surface, which is directed in a first phase towards the open end of the thread as well as the bottom part of the preform, is generated during the introduction of the cooling pins as well.
The new solution separates the secondary cooling into two independently controllable phases:
The new solution proposes to take advantage of various cooling interventions:
The invention is described in the following with a number of embodiments and additional details. They show:
FIGS. 17 to 17 d a solution with an expandable mandrel casing to calibrate and cool the inner side of the preform.
The greatest temperature drop in the injection moulds 10 from approximately 280° C. to 120° C. occurs still within the closed moulds 8 and 9, and an enormous through-put of cooling water must be ensured for this purpose. The removal device 11 is represented in dashes in a holding position, which indicates the end of the injection phase. The reference symbol 30 indicates the water cooling with the appropriate feed—and drain lines, which are shown in arrows for simplification; it is assumed that these are known. The reference symbol 31/32 indicates the air side, with 31 indicating the feed-in of blast air and/or compressed air and reference symbol 32 indicating a vacuum and/or suction air. In the injection moulds 8 and 9, the preforms are cooled simultaneously on the inside and outside while still in the injection cycle. Initially, only the outside is cooled in the cooling sleeves of the removal device 11. Another interesting issue is the handling in the area of the secondary cooling means 19. During the removal phase “A”, the secondary cooling means can be displaced independently horizontally according to arrow L from a pickup position into a drop position (shown in dashes). The secondary cooling means 19 has a multiple of capacity compared to the number of cavities in the injection mould halves. The drop of the completely cooled preforms 10 is therefore performed only after two, three or more injection moulding cycles so that the secondary cooling time is extended accordingly relative to the casting cycle. For the transfer of the preforms from the transfer gripper 12 to the secondary cooling means 19, the latter can be additionally displaced transversely and moved into the proper position.